Phase change materials (PCM) are substances with a relatively high heat-of-fusion or latent-heat capable of storing and releasing relatively large amounts of energy when they melt or solidify. PCM's may include inorganic salts, eutectic mixtures of inorganic salts, salt hydrates, fatty acids and esters, and various paraffins. Applications for PCM's include thermal systems in buildings, vehicles and spacecraft, thermal energy storage including solar thermal energy storage, solar central particle receivers or concentrating solar collectors, textiles, cooling and heating of electrical engines, cooling of foods and beverages, hot/cold therapies, waste heat recovery, etc.